The present invention relates to an electrical connector, and particularly to a zero insertion force (ZIF) connector having contacts which prevent molten solder from upwardly wicking along the contacts thereby achieving improved signal transmission.
A pertinent conventional connector relating to the present invention is a ball grid array (BGA) type connector. Referring to FIGS. 1A and 1B, a leg 80 of a contact (not labeled) of a conventional BGA connector (not shown) with a solder ball 89 attached thereto is shown. The leg 80 comprises an elongate connection portion 81, and a pad 82 for being surface mounted to a circuit board (not shown). The connection portion 81 is integrally formed with the pad 82 and a pair of cutouts 820 is defined proximate a junction between the connection portion 81 and the pad 82 on opposite sides of the connection portion 81. The solder ball 89 is attached to a bottom surface 822 of the pad 82.
When the BGA connector is heated to be surface mounted to the circuit board, the solder ball 89 melts and wicks upward along the soldering portion 81 via the cutouts 820 of the contact. Molten solder 88 may wick along the soldering portion 81 toward a contact tabs of the contact thereby adversely affecting signal transmission.
Moreover, wicking of the molten solder 88 causes the solder ball 89 to become smaller. Thus, the solder balls 89 attached to corresponding contacts do not remain in a common plane thereby decreasing the effectiveness of a soldering connection between the connector and the circuit board.
Another conventional connectors adapted for electrically connecting an IC package with a circuit board are disclosed in Taiwan Patent Application Nos. 83214436 and 86302100. Referring to FIGS. 2A and 2B, a conventional ZIF connector comprises a dielectric base 90, a slidable cover 91 fixed to the base, a cam lever 92 attached between aligned side edges of the base 90 and the cover 91 for driving the cover 91 to slide along a top surface of the base 90, and a plurality of contacts 93 received in corresponding contact receiving passageways 901 defined in the base 90.
Each contact 93 comprises a base plate 930, a curved portion 931 extending from a lower edge of the base plate 930, and a connecting leg 94 downwardly extending from the base plate 930 for electrically connecting with a circuit board (not shown). The curved portion 931 has a pair of curved arms (not labeled) separated from each other at the lower edge of the base plate 930 and connecting with each other at free ends thereof. The curved portion 931 defines a wide gap 9320 adjacent to a narrow gap 9321, and a pair of flanges 933 inwardly projecting from a junction between the wide gap 9320 and the narrow gap 9321. When the IC package (not shown) is positioned on the cover 91, pins of the IC package are disposed in the center of the wide entries 9320 of the corresponding contacts 93. With the sliding movement of the cover 91 driven by the cam lever 92 along the top surface of the base 90, the pins will be driven to move from the wide gaps 9320 into the narrow gaps 9321 guided by the flanges 933. Thus, the pins of the IC package electrically contact the corresponding contacts 93 of the ZIF connector.
However, when the contacts 93 are soldered to a circuit board (not shown), molten solder is apt to upwardly wick along the connecting legs 94 of the contacts 93 thereby adversely affecting signal transmission.
Furthermore, the symmetrical design of the conventional contact 93 usually provides a pair of symmetrical guiding portions such as the curved arms of the contact 93 to contact the corresponding pin of the IC package. Thus, frictional forces exerted on the pins are simultaneously applied by both the symmetrical curved arms thereby greatly increasing resistance which hinders proper positioning of the pins. The greatly increased resistance may wear a metal plating coat on the pins and the contacts thereby resulting in poor signal transmission.
In addition, the pins of the IC package may not be properly disposed in the corresponding pin receiving passageways of the cover 91, so that the pins will not be positioned in the center of the corresponding wide gaps 9320. Thus, when the pins are driven to move from the wide gaps 9320 into the narrow gaps 9321, a pin may only contact a single curved arm whereby the single curved arm may be burdened with too large a force, which may break the single arm, resulting in poor electrical connection.